Recovery Property On Compressive Strength Of Desert Sand Concrete(DSC)after High Temperature

The study of desert sand concrete(DSC)compressive strength after high temperature is very important for the study of DSC mechanical properties and its post-disaster evaluation.In this paper,the C50 DSC compressive strength after high temperature and the compressive strength after secondary curing were experimentally studied.The influence of desert sand replacement rate(DSRR),temperature,cooling method and secondary curing method on DSC mechanical properties after high temperature is analyzed,and a model of DSC compressive strength degradation after high temperature was further established.Through the ultrasonic testing test,the change law of DSC ultrasonic velocity after high temperature was studied.The influence of temperature,re-curing method and re-curing age on DSC compressive strength recovery were analyzed.The main research contents were as follows:(1)DSC was thermally damaged by high temperature test firstly,and the 12 groups of DSC conpressive strength test after high temperature has been completed on the basis of conpressive strength test at room temperature.The influence of temperature,DSRR,fly ash content and cooling method on DSC compressive strength was analyzed,and the degradation law of DSC compressive strength was summarized.The test results show that DSC mass loss rate increased at elevated temperature,DSC compressive strength shows a decreasing trend during the heating process,with increasing DSRR,DSC compressive strength increased first and then decreased after high temperature.When DSRR was 40%,DSC compressive strength reached to the maximum value.DSC has higher compressive strength under natural cooling at 100℃ and 300℃,and DSC compressive strength at 500℃and 700℃ was higher under water cooling.(2)Through DSC secondary curing test after different temperatures,the influence of temperature,secondary curing method and ages on DSC compressive strength after high temperature was analyzed.The test results show that,compared with DSC compressive strength after high temperature,DSC compressive strength was increased after secondary curing.with the curing age increased,DSC compressive strength increased first and then decreased after secondary curing.DSC compressive strength had the best recovery effect,which was cured by water,The compressive strength of DSC after air curing was lower than that of DSC under water curing.(3)Through non-destructive testing of DSC after high temperature by ultrasonic wave method,the influence of temperature on the DSC ultrasonic velocity was analyzed.Damage degree is proposed to measure the DSC damage degree and the relationship between relative ultrasonic velocity and damage degree was analyzed.A three-dimensional relationship model was established with respect to temperature,DSRR and relative ultrasonic velocity.The test result shows that,the DSC ultrasonic velocity was gradually dropped with the increase of temperature.Compared with DSC ultrasonic velocity after water cooling,the ultrasonic speed was increased more after natural cooling.(4)Through SEM scanning electron microscope test of DSC after high temperature and re-curing,DSC microscopic analysis under different temperatures and curing methods was carried out.The effects of temperature and re-curing method on the microstructure of DSC and the formation mechanism of internal hydration products of DSC after re-curing were studied.The mechanism of the re-curing on DSC strength recovery was explained from a microscopic point of view.